1. Field of the Invention
The present invention relates to wireless networks, more specifically to dual-mode wireless telephone communication networks that overlay digital cellular systems over existing analog-based cellular systems.
2. Background Art
Wireless telephone communication systems have evolved from the Advanced Mobile Phone Service (AMPS) technology, introduced around 1983, to more sophisticated digital-based air interface protocols. Specifically, the AMPS technology is an analog-based technology that uses frequency division multiple access techniques to divide the available radio spectrum into channel bandwidths, where each 30 kilohertz voice channel supports a single conversation. The AMPS system includes a plurality of base stations transmitting voice channels within the 800 MHz cellular band into overlapping propagation regions, also referred to as cells, to establish a cellular-based coverage area.
Digital access technologies have been developed based on Time Division Multiple Access (TDMA) or Code Division Multiple Access (CDMA) schemes. These digital access technologies are more efficient relative to analog-based access technologies such as AMPS. In TDMA, the RF carrier is divided into time slots. The digital system allocates speech to these time slots by converting and compressing speech information carried by analog voice signals into compressed digital samples using vocoding techniques, enabling the speech samples to fit into the time slots. Hence, 3 or more time slots may fit into each 30 kHz channel, resulting in at least a three-fold increase in capacity. The well-recognized TDMA-based GSM standard utilizes 8 time slots in 200 kHz bandwidth channels.
Code Division Multiple Access (CDMA) is an even more efficient access technology, where the compressed speech samples are spread over a large frequency band by coding each speech sample with a unique pseudorandom sequence. Multiple voice samples can then be sent through the same wide-frequency band. The digital wireless telephone having the correct pseudorandom sequence will reproduce the corresponding speech sample, whereas voice samples transmitted with different pseudorandom sequences will appear as background noise in the frequency band.
Hence, digital access technologies have substantial advantages over analog-based systems. Digital cellular systems, however, have not yet been deployed in as many regions as AMPS-based systems. Hence, digital cellular subscribers are offered continuous coverage using dual-mode wireless telephones capable of switching between a first mode (e.g., CDMA) and a second mode (e.g., AMPS) based on the availability of a certain technology.
Current dual-mode digital telephones are configured for initially searching for the preferred and digital technology, such as CDMA. Hence, the dual-mode wireless telephones will connect to an alternative technology (e.g., AMPS) only if the dual-mode digital telephone is unable to establish a link with the preferred digital (e.g., CDMA) technology. Hence, the dual-mode telephone will always try to look for the preferred CDMA technology first.
One problem encountered in digital cellular systems is that the digital wireless communication system may encounter a traffic condition that results in a system overload in the digital wireless communication system. For example, the number of CDMA telephone users may exceed a certain number that results in an unacceptably high level of system noise in the common air interface, also referred to as the airlink interface. Alternatively, atmospheric conditions may cause interference overload of the airlink. Alternatively, a hardware failure in a base station or within the switching matrix of the digital wireless communication system may reduce the capacity of the digital wireless communication system, resulting in system blockage on the digital wireless communication system.
One possible solution to overcoming the blockage problem in the digital wireless communication system is to transfer an existing telephone call by a dual-mode telephone from the CDMA-based system to the alternative AMPS-based system using a hard handoff protocol. The hard handoff from the CDMA-based system within the dual-mode system to the AMPS-based system is one of the most complicated and signaling-intensive procedures in wireless networks, especially since the dual-mode wireless telephone must switch from the digital mode to analog mode simultaneously with the hard handoff. Hence the hard handoff from the CDMA system to the AMPS system has a substantial risk in dropping the call.
In addition, attempts to transfer a CDMA-based wireless telephone call initiated by dual-mode telephone to an analog system requires the dual-mode telephone and the analog-based AMPS system to effectively reinitiate the telephone call before the calls go through, resulting in a substantially long time for call completion when a dual-mode wireless telephone user places a call.
There is a need for an arrangement that minimizes the occurrence of a dropped call and minimizes call setup time by a dual-mode telephone in a dual-mode digital cellular system encountering traffic or overload conditions.
There is also a need for an arrangement that enables a dual-mode telephone system to redirect dual-mode telephones to access an alternative wireless telephone system based on detected traffic conditions in the digital wireless communication system.
These and other needs are attained by the present invention, where a dual-mode wireless communications system, having a digital wireless communications system and a second wireless communications system, selectively outputs a control command from the digital wireless communications system to at least one selected dual-mode wireless telephone based on a detected traffic condition in the digital wireless communication system. The control command, output to a selected dual-mode wireless mode telephone having registered with the digital wireless communication system, instructs the selected dual-mode wireless telephone to register with the second wireless communication system, for example when the dual-mode wireless telephone is in an idle state. Hence, the digital wireless communication system can selectively limit access by the dual-mode digital telephones by outputting a control command to selected dual-mode telephones to register with the second wireless communication system. Consequently, dual-mode telephones can be proactively configured to access the alternative wireless communication system during detected traffic conditions in the digital wireless communication system, avoiding any handoff or registration steps that normally would be encountered upon initiating a wireless telephone call on the digital wireless communication system.
According to one aspect of the present invention, a method is provided in a dual-mode wireless communication system having a digital wireless communication system overlying a second wireless communication system. The method includes detecting a prescribed traffic condition in the digital wireless communication system, and outputting a control command based on the detected traffic condition. The control command is output from the digital wireless communication system to at least one selected dual-mode wireless telephone that has registered with the digital wireless communication system. The control command instructs the dual-mode wireless telephone to register with the second wireless communication system. Hence, a dual-mode telephone can be proactively controlled to search for an alternate system based on the digital wireless communication system detecting a prescribed traffic condition.
Use of the control command enables the digital wireless communication system to redirect the selected dual-mode wireless telephone to register with the alternative wireless communication system while in an idle state (i.e., when a call is not is progress). Hence, dual-mode wireless telephones can be easily transferred to alternative wireless communication systems without the necessity of a hard handoff procedure, or a reinitiation to the other system during call set up by the dual-mode wireless telephone on the digital wireless communications system.
Another aspect of the present invention provides a method in a wireless communication system including at least one dual-mode wireless telephone and a dual-mode communication system. The dual-mode communication system has a first wireless communication system and a digital wireless communication system overlying the first wireless communication system. The method includes establishing a first wireless link between the dual-mode wireless telephone and the digital wireless communications system according to a prescribed digital wireless protocol. A prescribed traffic condition is detected in the digital wireless communication system, and a control command is transmitted to the dual-mode wireless telephone on the first wireless link based on the detected prescribed traffic condition. The dual-mode wireless telephone, in response to reception of the control command, establishes a second wireless link with the first wireless communication system during an idle telephone state and according to a prescribed wireless protocol and drops the first wireless link. The detection of a prescribed traffic condition in the digital wireless communication system enables the proactive generation of the control command before an actual overload condition is encountered on the digital wireless communication system. In addition, the establishment of a second wireless link by the dual-mode wireless telephone during an idle telephone state enables the dual-mode wireless telephone to register with the first wireless communication system when a call is not in progress, minimizing the necessity for extensive signaling normally encountered when attempting to transfer the dual-mode wireless telephone from the digital wireless communication system to the first wireless communication system during call set-up or handoff.
Still another aspect of the present invention provides a dual-mode wireless communication system. The system includes a first wireless telephone communication system configured for wireless telephone communications in prescribed coverage areas according to a first wireless protocol, and a digital wireless telephone communications system. The digital wireless telephone communications system is configured for communication with dual-mode wireless telephones registered in the prescribed coverage areas according to a digital wireless protocol. The digital wireless telephone communications system includes a mobile telephone switching office configured for outputting a rescan instruction to a selected group of the dual-mode wireless telephones in response to detection of a prescribed condition in the digital wireless telephone communications system. The rescan instruction instructs the selected group of the dual-mode wireless telephones to register with the first wireless telephone communications system. Moreover, the selection of the group of dual-mode wireless telephones enables the mobile telephone switching office to proactively transfer certain dual-mode wireless telephones to the first wireless telephone communications system, while maintaining other dual-mode wireless telephones within the digital wireless telephone communications system. In this manner, the invention may provide a priority-based transfer of dual-mode wireless telephones based on different traffic conditions encountered by the digital wireless telephone communications system. For example, a low-priority group of dual-mode telephones may be transferred during moderate traffic conditions, whereas a majority of dual-mode wireless telephones are transferred during severe traffic conditions, reserving the digital wireless telephone communications system for high-priority dual-mode wireless telephone subscribers, such as premium service subscribers or emergency/test subscribers.
Yet another aspect of the present invention includes a dual-mode wireless telephone. The dual-mode wireless telephone includes a digital wireless transceiver configured for detecting a digital communications system and in response establishing a digital communication link according to a digital wireless protocol. The telephone also includes a second wireless transceiver, and a controller. The second wireless transceiver is configured for selectively establishing a wireless communications link with a second communications system according to a second wireless protocol. The controller is configured for activating the second wireless transceiver, during an idle telephone state, to establish the wireless communications link in response to reception of a rescan command via the digital communication link. Unlike conventional dual-mode wireless telephones that maintain communications with the digital communications system until forced to perform an intersystem handoff, the dual-mode wireless telephone of the present invention is configured for activating the second wireless transceiver during an idle telephone state in response to reception of a rescan command via the digital communication link. Hence, the dual-mode wireless telephone provides a convenient arrangement for establishing registration with the second communication system before the dual-mode wireless telephone is next used by the subscriber.
Additional advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.